X-ray apparatus



Sept- 6, 1955 A. A. NEMET ET AL X-RAY APPARATUS 2 Sheets-Sheet 1 FiledNov. 27 1951 Sept. 6, 1955 A. A. NEMET ET AL X-RAY APPARATUS Filed Nov.27, 1951 2 Sheets-Sheet 2 AM I '* INVENTORS Q. AMT/10mg Anfa/ NemefMatthew BerindeL BY United States Patent X-RAY APPARATUS Anthony AntalNemet, Richmond-Surrey, and Matthew Berindei, Cheam-Surrey, England,assignors to Hartford National Bank and Trust Company, Hartford, Conn.,as trustee Application November 27, 1951, Serial No. 258,338

Claims priority, application Great Britain November 28, 1950 3 Claims.(Cl. 250-95) This invention relates to X-ray apparatus of the typehaving an X-ray tube which, when in operation, takes a heavy current fora short period of time, and relates particularly to high-tension voltagesupply arrangements for X-ray apparatus of this type.

The voltage required for the energisation of an X- ray tube fordiagnostic radiography are usually of the order of 50 to 120 kv. andwith existing arrangements the X-ray exposures are normally taken withheavy currents from the supply mains lasting for a fraction of a second.For chest exposure, the instantaneous power may be of the order of 20-40kw.

The wiring, not only inside the apparatus but also to the points ofsupply, must consequently be heavy enough to carry without excessivevoltage drop the heavy currents involved. Consequently, in manyhospitals, special wiring has to be installed for the operation of theX-ray apparatus. In any event, the power station and the associatedtransmission system is subjected to instantaneous shocks.

To obviate these difliculties X-ray apparatus has been devised whichworks on the condenser storage principle, using high-tension condensersand associated high-tension switchgear.

The object of the present invention is to provide means for obviatingthe difiiculties without the use of hightension condensers.

According to the present invention, an X-ray apparatus having an X-raytube which, when in operation, takes a heavy current for a short periodof time, has the hightension supply for the X-ray tube obtained from theoutput of an electric generator driven by an electric motor.

Thus, the mains supply is used solely to energise the electric motorwhich in turn drives the generator from which the power is derived toenergize the X-ray tube.

With this arrangement, it is possible to use a relatively small electricmotor for example, a squirrel cage or a capacitor type motor, which isincapable of driving the generator at its operating speed when thegenerator is under load, but is able to run the generator up to speed ina short time when the generator is off lead.

Thus, when it is desired to make an X-ray exposure, the motor is firstswitched on and when the motor-generator system has run up to fullspeed, the generator is connected to the load. The kinetic energy of therotating system is used to supply the heavy load during the operation ofthe X-ray tube and, although the speed of the generator is slightlyreduced by the impressed load, the kinetic energy of the rotating systemis sufficient to prevent the speed of the generator, and hence thegenerator output from being reduced below a satisfactory working valueduring the period of an exposure.

If desired, the small driving motor may be disconnected from the mainssupply before the exposure begins but, even if it remains connected, theincrease of power taken from the mains is small, instantaneous peakloads on the supply mains are avoided and a normal wiring installationis adequate to carry the mains current to the motor.

2,717,315 Patented Sept. 6, 1955 The high-tension supply apparatus maybe installed separately from the part of an X-ray installation in whichthe X-ray tube is situated and an X-ray high-tension supply unitaccording to the invention has a supply obtained from the output of anelectric generator driven by an electric motor in the manner describedabove.

The electric motor may be driven either from a D. C. or an A. C. supplymains.

The generator may be a high-voltage D. C. machine,

but, in general, the generator will be an A. C. machine of relativelylow voltage output from which the high-tension supply will be obtainedby means of a high-tension transformer and rectifier system. It ispreferable, therefore, for the generator to be a high-frequencyalternator with an output of 360-400 volts at a frequency of 400 to 500cycles per second and for the supply to be obtained from the outputthereof by Way of at least one transformer and a rectifier. By using ahigh frequency of the order referred to, instead of a supply frequencyof cycles per second, the weight and size aswell as the cost of both thegenerator and the high-tension transformer can be substantially reduced.

In many cases, it may be sufficient to provide some indication of thegenerator output which enables the operator of the apparatus to see whenthe generator has run up to speed before operating the X-ray tube. Forexample, a voltmeter, a frequency meter or a tachometer may be suppliedfor this purpose. However, for an apparatus of this kind, it is theusual practice for the period of operation of the X-ray tube to becontrolled by a time switch which is pre-set by the operator to give therequired exposure time and is switched into operation by the operatorwhen he requires the exposure to begin. For some applications it ispreferred to interlock the time switch with the generator output toprevent the commencement of an exposure until the generator has run upto speed.

This may be done by using a control circuit which is dependent upon thevoltage of the generator output or its frequency, when the generator isan A. C. machine, or simply by providing a time delay mechanism whichprevents the operation of the time switch until the motorgeneratorsystem has had time to run up to speed.

It is preferred, however, to interlock the time switch with thegenerator output by means of a frequency sensitive circuit whichprevents the operation of the X-ray tube until the generator is able toprovide the required operating output and hence has reached its normalfrequency rating for this purpose.

To this end, the output of the generator may be applied across a networkcomprising a series resonance circuit tuned to the required frequencyand a bridge-connecting rectifier in series, the rectifier output beingapplied to the input terminals of a magnetic amplifier having a triggercharacteristic, the output of which amplifier controls the operation ofthe time switch.

The filament current of the X-ray tube and that of the high-tensionrectifying valves associated with the hightension supply rectifier maybe derived in a number of alternative ways. Both may be derived from thelocal A. C. supply mains using suitable transformers and suitablestabilising arrangements if desired. Alternatively, the filament currentof the X-ray tube, which current is more critical, may be obtained fromthe A. C. supply mains, using a stabilising arrangement, while therectifying valve filament currents may be taken from the alternatorsupply of higher frequency. As a further alternative, both may be takenthrough suitable transformers from the high-frequency alternator supply.However, this last alternative requires a more elaborate stabilisingarrangement, particularly because the speed of the alternator will fallwhen under load and, for this reason, the

high-frequency source will not normally be used for supplying the X-raytube filament current. A still further arrangement is to use twoconvertors connected to the supply mains, one for the high-tensionsupply and one for the filament supplies. This latter arrangement isparticularly suitable for an installation intended for operation from aD. C. supply mains.

In order that the invention may readily be carried into effect, twoexamples will now be described in detail with reference to theaccompanying drawings of which:

Figure 1 is a schematic circuit diagram of an X-ray installation thehigh-tension supply apparatus of which uses a motor energised from an A.C. supply mains coupled to a high-frequency alternator, a voltmeterbeing provided across the high-frequency supply so that the operator mayknow when the generator output has risen to its working value and Figure2 is a schematic circuit diagram of a modified form of X-ray apparatusin which the time switch is interlocked with the generator output bymeans of a frequency sensitive device.

In the two figures, corresponding components are in dicated by the samereference numerals.

In Figure 1, an electric motor 1 is energised from an A. C. supply mains42 by way of an isolating switch 2 and is coupled to a high-frequencyalternator 3 providing an output at 360 volts, 450 cycles per second A.C. The generator 3 is provided with a voltage stabiliser 4. This may beof any suitable form to provide rapid compensation of the output voltageand a suitable stabiliser of this form is described in British patentspecification No. 568,185. This form of stabiliser has a voltage inputobtained from connections across the generator output and a load currentinput derived from the secondary winding of a load current transformer5. The voltage stabiliser 4 controls the current through the fieldwinding 6 of the generator 3 in order to maintain a substantiallyconstant voltage output when the generator 3 is under load. The outputof the generator 3 is con nected across the primary winding of anauto-transformer 7 and the required voltage is taken from the secondaryof the auto-transformer 7 at the adjustable tap 8. A voltmeter 9 isconnected across the output of the transformer 7 and serves to indicateboth when the output is of a required voltage, when the motor-generator13 has run up to speed, and also, when the adjustable tap 8 has beenset, when the motor-generator has attained its working speed after beingswitched on. The operator may therefore use the reading of thisvoltmeter to indicate when the X-ray apparatus may properly be broughtinto operation. The output of the auto-transformer 7 is connected to thepoles of an isloating switch 10, it).

A time switch 11, of known form, is used to control the moment when theX-ray tube of the apparatus is brought into operation and the time forwhich its operation continues. This time switch is energised from anelectric supply 39 and controlled by a control switch 13. It operatesthe isolating switch 719. 10 by means of a relay 12 so connecting thehigh-frequency supply to the input winding of a hightension transformer14 or disconnecting it therefrom.

The high-tension transformer 14 has two output windings 15 and 16connected together at their inner ends through a milliamrneter 17. Theouter end of the windings 15, 16 are connected across the input of abridgeconnected rectifier comprising four rectifying valves 18, 19, 29and 21 obtaining their filament supplies from four output windings of afilament transformer 22 having its primary connected through a seriesvariable resistance 23 to a supply 24, which may conveniently be thesame as the supply mains 42. The output of the bridge-con- 27 which mayconveniently be the same as the supplies 42 and 24.

In operation, the motor 1 is connected across the supply mains 42, byclosing the switch 2 and the rising electric output voltage is notedfrom the voltmeter 9. When this has reached a steady value suchadjustment of the tapping 8 as may be required may be made otherwise,the time switch, which it is assumed has already been set to provide thecorrect exposure time, may be switched on by closing switch 13. Thiscauses the switch 10, 19- to be closed and the generator outputconnected to the hightension transformer 14 and hence the load. TheX-ray tube is thus brought into operation and after the requisiteexposure time, which is determined by the time switch 11, the switch 10,10 isautomatically opened by the operation of the time switch and theX-ray tube 25 put out of operation. During the exposure period, a heavyload is imposed on the generator 3 which consequently has a highreaction load placed on it tending to slow it down. However, the kineticenergy of the motor-generator system prevents the slowing down effectfrom being such as to reduce the generator output below a satisfactoryworking value during the period of the exposure.

In the modified arrangement shown in Figure 2 a series resonant circuit,comprising a condenser 27, an inductance 28 and a series adjustableresistance 29, which is tuned to the frequency of the output of thegenerator 3 when it has reached its operating value, is connected inseries With a bridge-connected rectifier 30 across the output terminalsof the generator 3. The rectified output of the rectifier 30 isconnected to the input winding 31 of a magnetic amplifier 32 having twooutput windings 33, 34. These output windings 33, 34 are connected inseries with a bridge-connected rectifier 35 and a solenoid winding of anA. C. relay 36 across an A. C. supply 37, which may conveniently be thesame as the A. C. supply 42.

The rectified output of the rectifier 35 is connected across a winding38 of the magnetic amplifier 32 which provide a measure of reaction andthus provides the magnetic amplifier 32 with a trigger characteristic.The relay 36 operates the control switch 13 of the time switch 11.

When this modified form of the apparatus is operated, the motor 1 isconnected to the supply mains 42 as before and it will be assumed thatthe tapping 8 has been set as required and that the time switch 11 hasbeen adjusted to give the required exposure time. When the motorgenerator 1, 3 runs up to speed so that the generator output has reachedits operating value, the generator output has also reached its nominalfrequency rating to which the tuned circuit 27, 28 and 29 is tuned. Inthis state, an A. C. potential is applied across the bridge rectifier 30and a D. C. input is provided to the magnetic amplifier 32. Owing to thecharacteristic of the tuned circuit, it will be appreciated that theinput to the magnetic amplifier 32 rises rapidly as the generator runsup to its operating speed. The input to the magnetic amplifier causes anA. C. potential to be applied across the bridge-connected rectifier 35and the D. C. output of this rectifier applied to the winding 38supplements the effect of the winding 31 so that a trigger effect isobtained and a sufiiciently high current fiows through the seriescircuit comprising the windings 33, 3 the bridge-connected rectifier 35and the relay 36 to operate the relay and hence to close the controlswitch 13. The time switch 11 is thus put into operation closing theswitch 10, 10 and putting the X-ray tube 25 into operation for therequired exposure time as in the form of the apparatus previouslydescribed.

What we claim is:

1. X-ray apparatus comprising an X-ray tube having a given power rating,a source of high-tension potential connected to said tube, saidpotential source comprising an electric generator having a power ratingof sufficient magnitude to supply said given power to said tube whenrunning substantially at its operating speed, a small electric motorcoupled to said generator for driving the same, said motor having apower rating substantially below that of said generator whereby it canonly drive said generator at its operating speed when the latter isunloaded, means for separately energizing said motor when said generatoris unloaded to bring said generator to its operating speed, and meanscoupling the output of said generator to said tube only when saidgenerator is running at its operating speed.

2. X-ray apparatus comprising an X-ray tube adapted to take a givenpower, a source of high-tension potential connected to said tube, saidpotential source comprising an electric generator having a power ratingof sufficient magnitude to supply said given power to said tube whenrunning substantially at its operating speed, a small electric motorcoupled to said generator for driving the same, said motor having apower rating substantially be low that of said generator whereby it canonly drive said generator at its operating speed when the latter isunloaded, means for separately energizing said motor when said generatoris unloaded to bring said generator to its operating speed, time switchmeans responsive to the speed of said generator coupling the output ofsaid generator to said tube and adapted to be actuated to supply powerto the latter only when said generator is running at its operatingspeed, and a frequency sensitive circuit coupled to the output of saidgenerator and adapted to actuate said switch means only when saidgenerator is running at its operating speed.

3. X-ray apparatus as claimed in claim 2 in which the frequencysensitive circuit includes a series-resonant circuit coupled to saidgenerator and tuned to the frequency produced by said generator whenrunning at its operating speed, a bridge-connected rectifier coupled tosaid resonant circuit, and a magnetic amplifier having a triggercharacteristic connected between said rectifier and said switch meansand adapted to actuate the latter.

References Cited in the file of this patent UNITED STATES PATENTS2,094,141 Zingg Sept. 28, 1937 2,140,707 Lee Dec. 20, 1938 2,488,167Brown Nov. 15, 1949 2,488,168 Brown Nov. 15, 1949 2,542,638 Desch Feb.20, 1951

